A “single-chamber heart stimulator” is generally understood to refer to a heart stimulator that is able to receive an intracardial electrocardiogram from only one ventricle via a corresponding sensing electrode, and to deliver stimulation pulses only to this ventricle via a corresponding stimulation electrode. Such stimulation and sensing electrodes can be distinct from each other, or can be formed by the same electrode pole. However, a single-chamber heart stimulator can also be a heart stimulator capable of connection to sensing electrodes in multiple ventricles, and which can therefore function as a multi-chamber heart stimulator; however, in operation, it is only connected to one electrode lead for sensing and stimulation in one ventricle.
One advantage of this type of single-chamber heart stimulator is its fundamentally simple design, coupled with the fact that only one single electrode lead has to be implanted in the heart of a patient.
Currently, multiple algorithms are known for discriminating between treatment-necessary ventricular tachycardias (VT) and supraventricular tachycardias (SVT) that do not require therapy. These kinds of algorithms are available in the implantable cardioverters/defibrillators (ICDs) of all manufacturers, and their effectiveness (sensitivity/specificity) has been demonstrated in clinical trials. However, such currently known algorithms are used in so-called two-chamber or three-chamber ICDs, since these always require information from the atrium as well.
There are various supplemental criteria for improving detection (sudden onset, stability, various QRS morphology criteria) for single-chamber ICDs, i.e., those without an implanted electrode in the atrium. In terms of the expected sensitivity/specificity, however, these criteria have limited effectiveness and are not able to distinguish all forms of VTs from SVTs. In particular, the use of morphology criteria has failed to demonstrate specificity improvement in multiple past clinical trials.